Detergent compositions have long employed materials, known as "builders", to improve the detergency of soaps and synthetic detergents by actively chelating alkali metal cations which are normal components of "hard" tap water. Such builders have been found to affect, for instance, soil suspension, emulsification of soil particles, solubilization of water-insolubles, and inactivation of various mineral constitutents present in a detergent system. Many materials useful as builders have been proposed, and their effects are known. See, e.g., U.S. Pat. Nos. 3,852,213, 3,950,260, 4,182,718, and 4,440,646 (all incorporated herein by reference).
Recently, however, the attention of detergent manufacturers and researchers has turned.to the role of heavier metal cations, i.e., transition metal cations, in the formation of stain complexes on fabrics and other surfaces. It has been observed that these multivalent transition metal cations, particularly iron (Fe.sup.+++, enhance the binding of the components of many stains to substrates, and breaking up the cation-enhanced bonds is an effective approach to stain removal. Therefore, there is a strong need for the discovery of new materials that are effective as chelating agents for transition metal cations, are easy to prepare, and can be added to detergent compositions in economical amounts to boost stain-removing power.
It has now been discovered that certain cyclic N-hydroxyimide compounds derived from substituted phthalic anhydride are active metal ion chelants and are useful as detergent additives. The N-hydroxyphthalimides of the present invention are water-soluble and form soluble chelates with transition metal ions which hinder detergent action and form stain complexes on fabrics and other substrates. In basic solutions, e.g., above about pH 9, ring-opened derivatives of the N-hydroxyphthalimides are believed to be produced, yielding carboxy hydroxamic acid-functional derivatives which are active metal ion chelants as well.